codegen: Properly detect bindgen unions.

The root cause of the issue was the missing:

```
  self.saw_bindgen_union |= new.saw_bindgen_union;
```

But I also cleaned up a bit more and removed the unused saw_union.

Fixes #1457

3 files changed, 107 insertions, 15 deletions

diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index d2b77d6a..9a7bf897 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -95,9 +95,6 @@ struct CodegenResult<'a> {
     /// Whether a bindgen union has been generated at least once.
     saw_bindgen_union: bool,
 
-    /// Whether an union has been generated at least once.
-    saw_union: bool,
-
     /// Whether an incomplete array has been generated at least once.
     saw_incomplete_array: bool,
 
@@ -140,7 +137,6 @@ impl<'a> CodegenResult<'a> {
     fn new(codegen_id: &'a Cell<usize>) -> Self {
         CodegenResult {
             items: vec![],
-            saw_union: false,
             saw_bindgen_union: false,
             saw_incomplete_array: false,
             saw_objc: false,
@@ -154,12 +150,7 @@ impl<'a> CodegenResult<'a> {
         }
     }
 
-    fn saw_union(&mut self) {
-        self.saw_union = true;
-    }
-
     fn saw_bindgen_union(&mut self) {
-        self.saw_union();
         self.saw_bindgen_union = true;
     }
 
@@ -221,11 +212,11 @@ impl<'a> CodegenResult<'a> {
 
         cb(&mut new);
 
-        self.saw_union |= new.saw_union;
         self.saw_incomplete_array |= new.saw_incomplete_array;
         self.saw_objc |= new.saw_objc;
         self.saw_block |= new.saw_block;
         self.saw_bitfield_unit |= new.saw_bitfield_unit;
+        self.saw_bindgen_union |= new.saw_bindgen_union;
 
         new.items
     }
@@ -1047,6 +1038,7 @@ impl<'a> FieldCodegen<'a> for FieldData {
 
         // NB: If supported, we use proper `union` types.
         let ty = if parent.is_union() && !parent.can_be_rust_union(ctx) {
+            result.saw_bindgen_union();
             if ctx.options().enable_cxx_namespaces {
                 quote! {
                     root::__BindgenUnionField<#ty>
@@ -1241,6 +1233,7 @@ impl<'a> FieldCodegen<'a> for BitfieldUnit {
         let field_ty = {
             let ty = helpers::bitfield_unit(ctx, self.layout());
             if parent.is_union() && !parent.can_be_rust_union(ctx) {
+                result.saw_bindgen_union();
                 if ctx.options().enable_cxx_namespaces {
                     quote! {
                         root::__BindgenUnionField<#ty>
@@ -1592,11 +1585,6 @@ impl CodeGenerator for CompInfo {
                 }
             }
         } else if is_union && !self.is_forward_declaration() {
-            result.saw_union();
-            if !self.can_be_rust_union(ctx) {
-                result.saw_bindgen_union();
-            }
-
             // TODO(emilio): It'd be nice to unify this with the struct path
             // above somehow.
             let layout = layout.expect("Unable to get layout information?");
diff --git a/tests/expectations/tests/bindgen-union-inside-namespace.rs b/tests/expectations/tests/bindgen-union-inside-namespace.rs
new file mode 100644
index 00000000..b2e6226c
--- /dev/null
+++ b/tests/expectations/tests/bindgen-union-inside-namespace.rs
@@ -0,0 +1,96 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
+pub mod root {
+    #[repr(C)]
+    pub struct __BindgenUnionField<T>(::std::marker::PhantomData<T>);
+    impl<T> __BindgenUnionField<T> {
+        #[inline]
+        pub fn new() -> Self {
+            __BindgenUnionField(::std::marker::PhantomData)
+        }
+        #[inline]
+        pub unsafe fn as_ref(&self) -> &T {
+            ::std::mem::transmute(self)
+        }
+        #[inline]
+        pub unsafe fn as_mut(&mut self) -> &mut T {
+            ::std::mem::transmute(self)
+        }
+    }
+    impl<T> ::std::default::Default for __BindgenUnionField<T> {
+        #[inline]
+        fn default() -> Self {
+            Self::new()
+        }
+    }
+    impl<T> ::std::clone::Clone for __BindgenUnionField<T> {
+        #[inline]
+        fn clone(&self) -> Self {
+            Self::new()
+        }
+    }
+    impl<T> ::std::marker::Copy for __BindgenUnionField<T> {}
+    impl<T> ::std::fmt::Debug for __BindgenUnionField<T> {
+        fn fmt(&self, fmt: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
+            fmt.write_str("__BindgenUnionField")
+        }
+    }
+    impl<T> ::std::hash::Hash for __BindgenUnionField<T> {
+        fn hash<H: ::std::hash::Hasher>(&self, _state: &mut H) {}
+    }
+    impl<T> ::std::cmp::PartialEq for __BindgenUnionField<T> {
+        fn eq(&self, _other: &__BindgenUnionField<T>) -> bool {
+            true
+        }
+    }
+    impl<T> ::std::cmp::Eq for __BindgenUnionField<T> {}
+    #[allow(unused_imports)]
+    use self::super::root;
+    pub mod foo {
+        #[allow(unused_imports)]
+        use self::super::super::root;
+        #[repr(C)]
+        #[derive(Debug, Default, Copy)]
+        pub struct Bar {
+            pub foo: root::__BindgenUnionField<::std::os::raw::c_int>,
+            pub bar: root::__BindgenUnionField<::std::os::raw::c_int>,
+            pub bindgen_union_field: u32,
+        }
+        #[test]
+        fn bindgen_test_layout_Bar() {
+            assert_eq!(
+                ::std::mem::size_of::<Bar>(),
+                4usize,
+                concat!("Size of: ", stringify!(Bar))
+            );
+            assert_eq!(
+                ::std::mem::align_of::<Bar>(),
+                4usize,
+                concat!("Alignment of ", stringify!(Bar))
+            );
+            assert_eq!(
+                unsafe { &(*(::std::ptr::null::<Bar>())).foo as *const _ as usize },
+                0usize,
+                concat!("Offset of field: ", stringify!(Bar), "::", stringify!(foo))
+            );
+            assert_eq!(
+                unsafe { &(*(::std::ptr::null::<Bar>())).bar as *const _ as usize },
+                0usize,
+                concat!("Offset of field: ", stringify!(Bar), "::", stringify!(bar))
+            );
+        }
+        impl Clone for Bar {
+            fn clone(&self) -> Self {
+                *self
+            }
+        }
+    }
+}
diff --git a/tests/headers/bindgen-union-inside-namespace.hpp b/tests/headers/bindgen-union-inside-namespace.hpp
new file mode 100644
index 00000000..6a7d3a30
--- /dev/null
+++ b/tests/headers/bindgen-union-inside-namespace.hpp
@@ -0,0 +1,8 @@
+// bindgen-flags: --rust-target 1.0 --enable-cxx-namespaces
+
+namespace foo {
+  union Bar {
+    int foo;
+    int bar;
+  };
+}